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<h1>Erbium, Er</h1>

Erbium (Er) is a rare-earth element that is part of the lanthanide series. In its metallic form, erbium is silvery-white and relatively stable in air. It is widely known for its optical properties, particularly in the field of fiber-optic communications. Erbium-doped fiber amplifiers (EDFAs) are crucial components that boost the signal in long-haul optical communication networks. When doped into other materials like glass or crystal, erbium can absorb pump light at specific wavelengths and emit light at around 1.55 micrometers, which is the standard wavelength for optical communications. Additionally, erbium finds use in other photonic devices, such as lasers for medical and materials processing applications. While not commonly used in its pure metallic form for optics, its dopant capabilities make erbium indispensable in modern optical technologies.

<h2>External links</h2>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Erbium">Erbium - Wikipedia</a></li>
<li><a href="https://www.webelements.com/erbium/">Erbium - WebElements</a></li>
</ul>
